Warden of the West
From Asoiaf
The Warden of the West guards the west of the Seven Kingdoms. The position is traditionally held by the Lord of Casterly Rock. The current Warden is Tywin Lannister, Lord of Casterly Rock.
283 AL Tywin took part in the Sack of King's Landing together with Eddard Stark, Lord of Winterfell. Prince Aegon Targaryen was ripped from the breats of his mother Princess Elia and killed before her eyes. Ser Jaime Lannister killed Aerys II Targaryen, King of the Seven Kingdoms in the throne room. Aerys' pregnant queen Rhaella and their son Viserys III Targaryen fled to Dragonstone.
Tywin accepted to take Robert Arryn, Lord of the Eyrie as his ward, but was refused by Lady Lysa.